Blood Alcohol Calculator

Estimate blood alcohol concentration (BAC) with a Widmark-type model using beverage volume, alcohol percentage, body weight, distribution factor, elapsed time, and elimination rate.

Never use this estimate to decide whether to drive. BAC can differ materially from this model and may still be rising. If alcohol was consumed, use a sober driver, taxi, or public transportation. Call emergency services for trouble breathing, unconsciousness, seizures, severe confusion, or repeated vomiting.

Body and time assumptions

Weight unit
Body weight
Distribution factor
Custom factor
Hours since drinking began
Elimination assumption (% BAC/hour)

Drinks consumed

Enter the actual serving size and alcohol by volume (ABV) from the label. Set servings to zero to ignore a row.

Drink	Amount	Unit	ABV %	Servings
Drink 1
Drink 2
Drink 3
Drink 4

Model results

—Estimated BAC

—Widmark value before time deduction

—Pure alcohol entered

—US standard-drink equivalents

—Arithmetic time to 0.000% in this model

—Sensitivity illustration

Modeled decline if no more alcohol is consumed

Additional time	Modeled BAC

How the BAC estimate works

The calculator first converts each beverage to milliliters of pure ethanol. It uses an approximate ethanol density of 0.789 grams per milliliter:

Alcohol grams = beverage volume × ABV ÷ 100 × 0.789 × servings

A Widmark-type estimate then divides alcohol grams by body weight in grams and the selected distribution factor, converts the result to percent BAC, and subtracts the entered hourly elimination assumption:

Estimated BAC (%) = alcohol grams ÷ (weight grams × factor) × 100 − elimination rate × hours

Examples

One 12-US-fl-oz beer at 5% ABV contains about 14.0 g of alcohol, approximately one US standard drink.
One 5-US-fl-oz wine at 12% ABV also contains about 14.0 g.
One 1.5-US-fl-oz spirit at 40% ABV contains about 14.0 g.
Two 12-US-fl-oz beers at 5% contain about 28.0 g total.
A 500 mL beer at 5% contains about 19.7 g, more than one US standard drink.
Two beverages with the same volume can contain very different alcohol amounts when their ABV differs.

Why actual BAC may be different

Alcohol may still be absorbing, so actual BAC can rise after drinking stops.
Food, drinking pace, medications, illness, liver function, body composition, and individual metabolism affect results.
The distribution factor and elimination rate are population assumptions, not personal measurements.
Mixed drinks and pours often contain more alcohol than their names imply.
Legal limits vary by jurisdiction, age, license, and vehicle type; being below a limit does not mean unimpaired.
Only a properly administered breath or blood test can measure BAC; even those tests have procedures and uncertainty.

Sources and related calculators

The US standard-drink reference of 14 grams comes from the National Institute on Alcohol Abuse and Alcoholism. Impaired-driving safety information is available from the National Highway Traffic Safety Administration.

Use the Percentage Calculator for general percentages or the Calorie Calculator for a separate daily-energy estimate. Neither replaces medical or safety assessment.